Total world military spending was $1.7 trillion for 2015, an increase of 1 percent over 2014.

The Asia-Pacific region was largely responsible for the rise, with countries averaging a 5.4 percent increase in military expenditures. Heightening tensions between China and others in the region sparked "substantial" spending increases by Indonesia, the Philippines and Vietnam, SIPRI reported. The situation also caused Japan to reverse its long-term downward trend in military spending.

The U.S. was still the largest military spender at $596 billion, SIPRI said. While U.S. military spending decreased from 2014 to 2015, it did so at a slower rate of decline, 2.4 percent, than past years.

The second-largest spender was China. Beijing's figure for 2015 rose 7.4 percent to $215 billion. Saudi Arabia came in third, spending $87 billion, and Russia was fourth, spending $66 billion on its military.